FLOOD11149

• County: Jefferson
• County: Arapahoe
• Basin: South Platte
• Title: Chatfield Reallocation Study: Meeting Minutes 06/22/2005
• Date: 6/22/2005
• Prepared For: Meeting Participants
• Prepared By: CWCB
• Floodplain - Doc Type: Meeting Summary

STATE OF COLORADO

Colorado Water Conservation Board

Department of Natural Resources
1313 Sherman Street, Room 721
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]
www.cwcb.state.co.us

MEMORANDUM

Bill Owens
Governor

To:
From:

Chatfield Reservoir Reallocation Study Interested Parties
Larry Lang, CWCB Flood Protection Program
Joe Busto, CWCB Flood Protection Program
Monday, June 27, 2005
Meeting Summary from June 22nd Chatfield Study meeting at the Division of
Wildlife Offices

Russell George
Executive Director

Rod Kuharich
CWCB Director

Date:
Re:

Rick Brown
Acting Deputy Director

Attachments
. Corps June 21,2005 Working Draft Scope of Work for a Environmental Restoration Add to the
Corps-CWCB FCSA including SchedulelBudget Estimate
. Sign in sheets for the June 22nd meeting

Introduction
The Project Manager and CWCB Staff welcomed the participation of the Chatfield Working Group,
the Chair of the Chatfield Water Users Sub-Committee, the Corps of Engineers, and the representatives
of the many interested parties.

Antecedent Flood Study - Corps of En2ineers - Action Item NO.2 by Doug Clemenson
. Doug outlined the Corps' study procedure and base date for the analysis which are 1) collecting
and evaluating all the Colorado rainfall in amounts greater than a 10 inches and determine the
rainfall amount before the 10" plus occurrence note: preliminary findings is the value is 20%;
2) collecting and evaluating all the large snowfalls and make a determination regarding a
percentage before the large snowfall occurrence note: preliminary findings indicates a value of
40%; and 3) performing a Monte Carlo simulation which will extend the date sets over more or
less 10,000 years.
. Ifwe can lower the antecedent flood (inflow design flood) by 10% we can carve out the 20,600
AF additional storage space. The Corps is looking at historic snowmelt floods and the South
Platte River's natural stream flows.
. Discussion about including the Dillon Reservoir diversions into the analysis. The period of
record they are looking at will include the last 60 years, or 1942-2002 so therefore it does
include the Dillon Reservoir diversions. It is often approximately 600 cfs coming through the
tunnel.
. The existing Chatfield Reservoir flood operational release are: looking at flood event
operations through modeling. In the worst case, during a flood, the Corps shuts down for five
days. Then they ramp up releases by 500 cfs/day to 5,000 cfs total.
. One and two of three parts of the antecedent flood study are done. The third part of the study is
the Monte Carlo simulation that is not likely to change this situation. Weare on a favorable
path right now. The Monte Carlo simulation uses precipitation and stream flow combined. This

Flood Protection. Water Supply Planning and Finance. Stream and Lake Protection
Water Supply Protection. Conservation and Drough t Planning